1. Technical Field
The present invention relates to defective image detection methods and storage media storing programs.
2. Related Art
If dust is attached to an original, the images of such dust are included in the digital image of the original read by a scanner. For this reason, it is preferable to remove dust on an original with a blower or the like before the original is read. However, it is difficult to completely remove dust from the original.
Therefore, means is proposed for detecting dust images in a digital image to remove the same (see British Patent Publication No. 1547811, specification, JP-A-2003-101732 and JP-A-10-232915).
British Patent Publication No. 1547811, specification, discloses an apparatus for detecting dust on the original using infrared light. However, since provision of hardware such as an infrared light source is required, the apparatus becomes expensive.
JP-A-2003-101732 discloses a technique in which a binary image is subjected to a labeling process so as to enclose an individual image block with a rectangular frame. The image block enclosed with such a rectangular frame that falls under predetermined conditions is judged to be a dust image component. However, since a generation process of the binary images is not clear, it is not certain whether this technique is applicable to any type of image.
(1) Incidentally, while a dust image present in a low spatial frequency region is highly noticeable, a dust image present in a high spatial frequency region is less noticeable. In addition, other than the dust image, noise or the like present in a low spatial frequency region is highly noticeable and those present in a high spatial frequency region are less noticeable.
(2) When determination is made as to whether or not a given image in an original image is the dust image, if the same method is always used for such determination, erroneous detection of the dust image becomes more likely. In addition, when determination is made as to whether or not a given image in an original image is a defective image such as noise, which is not limited to the dust image, if the same method is always used for such determination, erroneous detection of the defective image becomes more likely.